ROUTES OF YOLK UTILIZATION IN THE NEWLY-HATCHED CHICK

1. This study was conducted to study the routes by which yolk is utili sed in the chick during the initial posthatch phase. 2. Transfer from yolk to blood was examined by injecting, in the form of labelled compo unds, oleic acid, triolein, inulin and dextran into the yolk; movement from yolk to blood was observed up to 72 h posthatch. 3. Transport of these molecules from blood to yolk was also observed by injecting the m into the circulation and determining label in yolk. The yolk. sac me mbrane was permeable in both directions for all labelled materials tes ted. 4. In the newly-hatched chick, blue dextran injected into the yol k sac could be seen moving in pulses into the intestine at irregular i ntervals. Transport of labelled materials from the yolk sac into the i ntestine was observed up to 72 h after hatching and marker was found i n the proximal small intestine and gizzard. The yolk stalk provided a pathway for transport to the intestine until lymphoid cells began to a ccumulate, with passage becoming partially occluded at 72 h posthatch. 5. Yolk utilisation was more rapid in fed than in fasted birds sugges ting that the transport of yolk through the intestine could be increas ed by the greater intestinal activity found in fed chicks.